We propose to study the mechanism(s) of potential production in the photoreceptors and the distal interneurons of the retina. Unlike the more conventional neurons, these cells respond to light stimuli with slow, graded responses. The mechanism of phototransduction will be investigated by means of electrophysiological techniques using photoreceptor mutants of Drosophila. The ionic and synaptic mechanisms will be studied on the horizontal and bipolar cells of the vertebrate retina. Attempts will be made to gain insight into the organization of the retinal circuitry.